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Lenses with short focus throw = more teeth on FF gears?


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#1 George A

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Posted 23 June 2016 - 05:12 PM

Hi!

 

Quick question about using the Arri FF4 Follow Focus on lenses with short focus throw and crowded markings.

 

The FF4 comes with the regular 0.8 gear which has 43 teeth:

 

https://www.zgc.com/...rri_381574.html

 

When using it on lenses with a very short focus throw - does it make sense to get the larger FF4 gear? It has a significantly larger diameter and has 64 teeth instead of 43:

 

https://www.zgc.com/...rri_381576.html

 

Would it help with the accuracy of pulling focus in a significant way? (by extending, in effect, the focus throw).

Does it make a palpable difference? Is it worth getting it?

 

Thanks so much!


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#2 Satsuki Murashige

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Posted 23 June 2016 - 05:32 PM

The larger gear can help with extending the focus throw, but whether it makes a useful difference in achieving a difficult shot (or not) really depends on the lens in question.

Some still photo lenses have such a short throw between infinity and say 6' that the larger gear won't help much. I have a Sigma 24mm f1.8 macro lens like that, the throw from infinity to 3' is maybe 10 degrees. I would say it is more useful for extending the focus throw on a lens like the Fujinon Cabrio 19-90, which already has something like 180 degrees of throw - fine for documentary but could use a bit more for narrative work.

If you really need to significantly extend the throw of a still photo lens, I would recommend getting a wireless follow focus device like the Preston F/I which will electronically map the entire focus throw of the lens to the full range on the hand unit. Then your AC can make new focus marks on the hand unit and pull with much more precision.
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#3 Ben Rowsell

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Posted 23 June 2016 - 08:36 PM

Increasing the gear size on the follow focus will gear it up and give you less turn on the focus wheel relative to the lens. You want to go the other way and gear down (smaller) so that any given amount of turn on the focus wheel gives you less turn on the lens, to be more accurate. I believe the smallest gear available is 35 teeth. Another way is to use a 2 speed system such as on the FF3, and put it into slow gear. That will effectively extend the range of the lens. Try and get a FF with no lag or the marks will be well off as you change direction.

 

The most effective way to do it as mentioned above by Satsuma is to use an electronic system that allows you to expand the range of the lens relative to the handset. This will be a lot more effective than gearing down a manual follow focus. Again, the smaller the gear size the better, so in theory something like a Heden M21, Preston DM4, or Cforce Mini with smaller gears will have to make more turns to get to the lens limits, so the resolution and accuracy will be a bit better than a standard motor

 

Ben R


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#4 Satsuki Murashige

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Posted 23 June 2016 - 08:55 PM

Oops, right you are Ben!
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